Transcript File - We All Love Science

Unit 8: Small Bodies around our
Sun
Mr. Ross Brown
Brooklyn School for Law and
Technology
In this unit we will learn about:
• The different types of small bodies in our Solar
System
• Meteorites and their origins
• Asteroids and dwarf planets
• Comets, their orbits, and their structures
• Results of collisions of these bodies with the
Earth
• The impact on Earth 65 millions years ago and
how it led to the demise of the dinosaurs
What small objects also orbit our Sun?
• 2 February 2016
• Do now: Why do we find so few meteorites
here on Earth?
What happens when meteors
approach the Earth?
• Meteor: a streak in the night sky made by
friction of a solid body passing through Earth’s
atmosphere; a shooting star
• Meteoroid: the solid body
• Meteorite: if it reaches the Earth
What happens when meteors
approach the Earth?
• As meteoroids enter our atmosphere they
encounter friction
• 10-40 km/ second
• Air resistance also slows them, so they can
land
What types of meteorites are there?
• Stony – silicates
– Composed of grains of rock (chondrules) stuck
together, thus called Chondrites
– Carbonaceous chondrites: chondrites in carbonrich substance, contains amino acids
What types of meteorites are there?
• Achondrites (without chondrites)
– Iron: show crystals, indicating they cooled over
millions of years
– Stony-iron: rare combination, perhaps from
mantle-core boundary of exploding asteroid
What makes an asteroid “an asteroid?”
• 3 February 2016
• Do now: Where did all those asteroids come
from?
What makes an asteroid “an asteroid?”
• Asteroids: small, rocky bodies 2-4 AU from the
Sun
• Aster: Greek for “star”
• Bode’s Law predicted a planet at 2.8 AU
• More than 100,000 found, but less than
1/1000 Earth’s mass
• Ceres is largest
Bode’s Law
What makes an asteroid “an asteroid?”
What makes an asteroid “an asteroid?”
• Ceres has enough mass to produce gravity to
make it a sphere; considered a dwarf planet
• Most are irregularly shaped
Eros
Itokawa
Vesta compared to other asteroids
Ceres
What makes an asteroid “an asteroid?”
• Many are iron or silicate but not all are solid
– Loose rubble held together by gravity
– Mathilde density 1.4, Itokawa 1.9
What makes an asteroid “an asteroid?”
• Composition
– Silicate, carbonaceous, or iron-nickel
• Inner-belt are mostly silicate-rich
• Outer-belt are mostly carbon-rich
What makes an asteroid “an asteroid?”
• Origins
– Solar Nebula Theory
• Inner planets silicate based, thus inner asteroids…..
Homework #14
• 3 February 2016
• What is the difference between a meteor, a
meteoroid, and a meteorite?
• What shape are typical asteroids and how do
we know? Why does Ceres not have this
shape?
Aim: What lies beyond Neptune?
• 4 February 2016
• Do now: Imagine you are in a rocket ship
racing past Neptune. What objects might you
encounter? What would these be made of?
What happened to Pluto?
• Trans-Neptunian Objects (TNOs): very small
objects orbiting our Sun beyond Neptune’s
orbit
• Pluto!
– Discovered in 1930 by reviewing photos to identify
objects whose position changed
Pluto
• Named after the god of the underworld
• Moon (Charon) discovered in 1978, named
after boatman who ferries dead souls across
the River Styx to the underworld
Pluto
• Originally thought to be about Earth-sized
• By studying Charon’s orbit  Pluto’s mass
– .002 Earth mass, 1/20 Mercury
– 1/5 Earth diameter
– Density 2.1
– Orbit intersects Neptune’s  is it a planet?
What defines a “planet?”
• International Astronomical Union (IAU) 2006
stated that a planet:
1. is in orbit around the Sun,
2. has sufficient mass to assume hydrostatic
equilibrium (a nearly round shape), and
3. has "cleared the neighborhood" around its orbit.
Which criterion does Pluto miss?
Plutoids
• Several hundred other objects kilometers in
diameter orbit as far as Pluto
– Sedna: 1000 km in diameter, well past Kuiper Belt
– Eris: 38-97 AU from Sun, 2400 km in diameter,
orbit inclined 44°
– Because of these, and its own orbit and size, the
International Astronomical Union defined Pluto
and other like bodies as dwarf planets
– Plutoids: dwarf planets that orbit our Sun
Plutoids
Plutoid Orbits
So, what are all the things in our Solar
System?
Aim: What are comets?
• 9 February 2016
• Do now: Of what are comets made? And from
where do they come?
What are comets?
• Once feared due to their mystery
What are comets?
• 3 parts
– Tail: long, narrow column of dust, can be 100
million km (almost 1 AU)
– Coma: cloud of gas, can be 100,000 km diameter
(10x Earth) but very little mass
– Nucleus: block of frozen ice and gas, about 10 km
Comet Halley
How do comets’ tails form?
• Comets aren’t visible unless within about 5
AU. Sun’s heat vaporizes ices into gases.
• Gases blown into an ion tail by solar winds.
This points away from the Sun.
How do comets’ tails form?
• Dust tail: radiation pressure from the Sun
pushes the dust coming off the comet.
Of what are comets made?
• 10 February 2016
• Do now: From where do comets originate?
Of what are comets made?
• How can we tell the composition of a comet?
– Fluorescence: wavelength of reflected light
• From dust from comets
Of what are comets made?
• 2005, NASA Deep Impact mission
– Smashed a probe (370 kg) into Comet Tempel 1 @
10 km/ sec
– Comet was made of water, silicates, clays
Of what are comets made?
• If comets pass too close to the Sun…….?
– SOHO Observatory shows dozens each year falling
into the Sun
Of what are comets made?
• Comet origins
– Oort Cloud: trillions of icy bodies far beyond
Neptune
• Surrounds the Solar System
Oort Cloud
Oort Cloud
Of what are comets made?
• Kuiper Belt
– Begins about Neptune’s orbit, out to ~ 50 AU
Of what are comets made?
• Oort Cloud comets may take millions of years
to orbit the Sun.
• Temperatures of 3°K or -454°F.
Of what are comets made?
• Most comets take millions of years to return
• Short-period comets
– Less than 200 years
– Kuiper Belt may contain more than 30,000
– Can they survive?
Homework #15
• 10 February 2016
• Explain the difference between the tail of a
meteor and the tail of a comet. Are they made
of the same things?
What have been the results of giant
impacts?
• 11 February 2016
• Do now: What would happen if a meteor 10 m
in diameter hit the Earth? 100 m? 1 km? 10
km?
Meteor Showers
• Asteroid fragments entering Earth atmosphere
from the same orbit. Appear to come from
constellation Perseus, hence Perseid Meteor
Shower in mid-August.
What have been the results of giant
impacts?
• This happens every few thousand years!
• 100 tons of meteoroids strike Earth every day
– Most are smaller and our atmosphere slows them
• However……
What have been the results of giant
impacts?
• Scars across our planet
– Arizona: 50,000 years ago, 50 meters across
– Impact crater 1.2 km across, 200 m deep
What have been the results of giant
impacts?
• 1908, north-central Siberia (Russia)
• Trees leveled for 30 km
What have been the results of giant
impacts?
• 65,000,000 years ago
– End of Cretaceous Period
– Iridium found in sediments
What have been the results of giant
impacts?
• Chicxulub Meteor
– 10 km across
– Equivalent to several billion nuclear weapons
– Mass extinction. Bye, bye dinosaurs!